Carbon contamination resistant pressure atomizing nozzles

ABSTRACT

A pressure atomizing nozzle for injecting fuel includes an inlet housing configured to thermally isolate the interior space from external conditions and to remain relatively cool under operation so as to substantially eliminate heat soak back from the inlet housing to the interior space thereof after operation. First and second coolant conduits cool the nozzle tip region actively during operation and passively after operation. A cooling air jacket is configured to thermally isolate inboard components from exterior conditions, to provide clean air during operation to the nozzle tip region for diluting carbon to reduce carbon deposits in the nozzle tip region and for cooling the same, and to provide passive cooling to the nozzle tip region after operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of co-pending U.S. patentapplication Ser. No. 13/247,199 filed Sep. 28, 2011, which claimspriority to and the benefits of U.S. Provisional Application Ser. No.61/387,746, filed Sep. 29, 2010, each of which are incorporated hereinby reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid injection nozzles, and moreparticularly, to pressure atomizing nozzles for injecting fuel forcombustion.

2. Description of Related Art

A variety of devices are known for injecting and atomizing liquids. Forexample, pressure atomizing nozzles can be used to inject an atomizedspray of fuel to be combusted in a furnace, gas turbine engine, or thelike. The harsh environment of combusting fuel gives rise todifficulties associated with the breakdown of fuel at high temperatures.Hydrocarbon fuels tend to decompose when heated. At elevatedtemperatures below about 800° F., dissolved oxygen in the fuel formscoke deposits. At temperatures above about 800° F., pyrolysis occursleading to carbon deposits. Coke deposits tend to form on internalnozzle surfaces, and carbon deposits tend to form on external nozzlesurfaces. Coke and carbon deposits are each described in greater detailbelow. These problems give rise to a need to replace or clean nozzlesoperating in combustion environments which results in expense and/ordowntime that could otherwise be avoided.

With respect to coke formation, intricate fuel passages of typicalatomizing nozzles are susceptible to the formation of coke when heatedto sufficient temperatures. This is particularly a problem when stagnantfuel in the fuel passages is heated, such as just after an engine isshut down, or when an engine is running with staged fuel injection sothat some fuel passages are stagnant during operation. Coke depositsaccumulate in nozzle tip openings and intricate fuel passages and ifleft unchecked can lead to inadequate flow and even complete blockage offlow.

With respect to carbon deposits, the deposition of carbon on exposednozzle surfaces, e.g., soot deposits, can occur wherever relatively coolsurfaces are exposed to combustion products. When fuel is runningthrough a typical nozzle with combustion occurring just downstream ofthe nozzle, the nozzle is cooled by the fuel flowing therethrough.Carbon released from the fuel by pyrolysis, coming into contact with therelatively cool exposed surfaces of the nozzle, can condense and form acarbon deposit thereon. Similar to coke deposits, carbon deposits canalter nozzle geometry and therefore hinder proper functioning.

Some solutions to these problems have been practiced with some success.For example, one approach is to use a local thermal heater tosystematically burn carbon and coke from the nozzle tip to keep thenozzle free of contamination. However, the heater approach is relativelyexpensive and introduces its own reliability issues.

Such conventional methods and systems have generally been consideredsatisfactory for their intended purposes. However, there is still a needin the art for nozzles that allow for improved reduction and/orprevention of carbon and coke deposition, including by passive means.There also remains a need in the art for such nozzles that are easy tomake and use. The present invention provides a solution for theseproblems.

SUMMARY OF THE INVENTION

The subject invention is directed to a new and useful spray nozzle forinjecting fuel. The spray nozzle includes an inlet housing having a fuelinlet and first and second coolant ports. The inlet housing defines aninterior space and is configured to thermally isolate the interior spacefrom external conditions during operation and to reduce heat soak backfrom the inlet housing to the interior space thereof after operation. Afuel conduit is mounted in the interior space of the inlet housing influid communication with the fuel inlet for providing fuel to a spraynozzle, e.g., a pressure atomizing nozzle, mounted to the fuel conduit.

In certain embodiments, a first coolant conduit is mounted in theinterior space of the inlet housing outboard of the fuel conduit and influid communication with the first coolant port of the inlet housing andwith a nozzle tip region proximate an outlet end of the spray nozzle. Itis also contemplated that a second coolant conduit can be mounted in theinterior space of the inlet housing outboard of the first coolantconduit and in fluid communication with the second coolant port of theinlet housing and with the nozzle tip region. The first and secondcoolant conduits are configured and adapted to conduct coolant from oneof the coolant ports to the nozzle tip region, and to conduct coolantfrom the nozzle tip region to the other of the coolant ports for coolingthe nozzle tip region actively during operation. The first and secondcoolant conduits are configured and adapted to conduct coolant passivelyto cool the nozzle tip region after operation.

For example, the first coolant port can be a coolant outlet, wherein thesecond coolant port is a coolant inlet. The second coolant conduit canbe configured and adapted to conduct coolant from the coolant inlet tothe nozzle tip region for cooling the nozzle tip region, and the firstcoolant conduit can be configured and adapted to conduct coolant awayfrom the nozzle tip region to the coolant outlet. It is alsocontemplated that a downstream tip region of the first coolant conduitcan include coolant metering slots for passage of coolant from thesecond coolant conduit into the first coolant conduit.

In accordance with certain embodiments, the fuel inlet is a first fuelstage inlet and the inlet housing includes a second fuel stage inlet. Asecond fuel conduit is mounted in the interior space of the inlethousing outboard of the first fuel conduit, inboard of the secondcoolant conduit, for example, and in fluid communication with the secondfuel stage inlet of the inlet housing for providing fuel to a secondspray nozzle mounted outboard of the first spray nozzle.

It is also contemplated that a cooling air jacket can be mounted to theinlet housing outboard of the second coolant conduit for conducting aflow of cooling air to the nozzle tip region, wherein the cooling airjacket is configured to thermally isolate inboard components fromexterior conditions, to provide clean air during operation to the nozzletip region for diluting carbon to reduce carbon deposits on the spraynozzle and for cooling the same, and to conduct air for passive coolingto the nozzle tip region after operation. The inlet housing and/or thecooling air jacket itself can include a cooling air inlet in fluidcommunication with an air flow circuit within the cooling air jacket forsupplying cooling air during operation. A heat shield can be mountedinboard of the cooling air jacket and outboard of a component inboard ofthe cooling air jacket, for example a second coolant conduit asdescribed above, to provide thermal isolation therebetween. The coolingair jacket can include an outlet aperture in proximity with the nozzletip region for providing an outlet for the spray nozzle and cooling air.

These and other features of the systems and methods of the subjectinvention will become more readily apparent to those skilled in the artfrom the following detailed description of the preferred embodimentstaken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that those skilled in the art to which the subject inventionappertains will readily understand how to make and use the devices andmethods of the subject invention without undue experimentation,preferred embodiments thereof will be described in detail herein belowwith reference to certain figures, wherein:

FIG. 1 is a cross-sectional perspective view of an exemplary exhausttreatment system incorporating a nozzle constructed in accordance withthe present invention, showing the flow of exhaust through the system;

FIG. 2 is a cross-sectional side elevation view of a prior art two-stagepressure atomizing nozzle, showing typical regions where coke and carbonaccumulate;

FIG. 3 is a cross-sectional side elevation view of the nozzle of FIG. 1,showing the thermal isolation inlet housing and conduits leading to thenozzle tip;

FIG. 4 is a perspective view of a portion of the nozzle of FIG. 3,showing the fuel and air inlets, and the coolant inlet and outlet of theinlet fitting;

FIG. 5 is a cross-sectional side elevation view of a portion of thenozzle of FIG. 1, showing the flow of coolant to and from the nozzletip;

FIG. 6 is a cross-sectional side elevation view of a portion of thenozzle of FIG. 1, showing the castellation in the tip end of the firstcooling conduit;

FIG. 7 is a cross-sectional side elevation view of a portion of thenozzle of FIG. 1, showing the nozzle spray and hot combustion gas duringoperation of the nozzle injecting fuel;

FIG. 8 is a cross-sectional side elevation view of a portion of thenozzle of FIG. 1, showing the flow of cooling air when the nozzle is notinjecting fuel;

FIG. 9 is a cross-sectional side elevation view of another exemplaryembodiment of a nozzle constructed in accordance with the presentinvention, showing the fuel and coolant conduits;

FIG. 10 is a perspective view of a portion of the nozzle of FIG. 9,showing the fuel inlets and the coolant inlet an outlet of the inletfitting;

FIG. 11 is a cross-sectional side elevation view of a portion of thenozzle of FIG. 9, showing the tip region and air inlets through thecooling air jacket;

FIG. 12 is a cross-sectional end view of the nozzle of FIG. 9, showingthe coolant return passages at the cross-section indicated in FIG. 11;and

FIG. 13 is a cross-sectional end view of the nozzle of FIG. 9, showingthe feed slots of the secondary fuel circuit at the cross-sectionindicated in FIG. 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings wherein like referencenumerals identify similar structural features or aspects of the subjectinvention. For purposes of explanation and illustration, and notlimitation, a partial view of an exemplary embodiment of a nozzle inaccordance with the invention is shown in FIG. 1 and is designatedgenerally by reference character 100. Other embodiments of nozzles inaccordance with the invention, or aspects thereof, are provided in FIGS.2-13, as will be described. The system of the invention can be used toreduce or eliminate coke and/or carbon deposits in nozzles, for example,nozzles used in combustion based heating devices or engines.

Referring to FIG. 1, an exhaust treatment system 1 is shown for treatingexhaust entering inlet 2 with unburned components. The untreated exhaustenters housing 3, where it must pass through filter 4. Filter 4 trapsparticulate matter and thereby cleanses the exhaust. Over time, filter 4becomes saturated with particulate matter filtered from the exhaust. Inorder to clear or regenerate filter 4, nozzle 100 can be activatedoccasionally, burning fuel therefrom as needed to raise the temperatureof filter 4. Engine fuel and air are supplied to nozzle 100 to producecombustion heat. The heat combusts trapped particulate matter and clearsfilter 4 for further use. After being filtered, the exhaust finallyexits system 1 through outlet 5. The treated exhaust can then beexpelled to the atmosphere having had a significant amount of theharmful pollutants removed by system 1. Exhaust treatment system 1 canbe used, for example, to treat diesel exhaust to reduce particulatematter emissions.

With reference to FIG. 2, the outlet end of a typical prior art duplexpressure atomizing nozzle 10 is shown. In certain applications wheresuch atomizing nozzles are used, such as system 1 described above,nozzle 10 is located in a heated gas stream even when fuel is notflowing through nozzle 10. For example in system 1, if prior art nozzle10 is used instead of nozzle 100 of the subject application, while inoperation in the interim between firings of nozzle 10, high temperatureexhaust filters past nozzle 10. When the combustion cycle is over, thehot inlet exhaust persists although at lower temperatures when thenozzle is not firing. Since the inlet exhaust is often above temperaturelevels known to destabilize hydrocarbon fuels, stagnant fuel in thetypical nozzles such as nozzle 10 is prone to coking in passages runningthrough the nozzle 10.

With continued reference to FIG. 2, nozzle 10 is also subject todetrimental coking conditions when nozzle 10 is firing only one of itstwo fuel circuits. This can be particularly detrimental to the stagnantsecondary channels (i.e., fuel passages 20) in the nozzle tip which arenot flowing while the primary fuel is still flowing to feed a flame. Theheat from the primary flame cokes the stagnant fuel in the secondarychannels. Surface tension holds fuel in the secondary flow distributor,e.g., around tip area 40 in FIG. 2 and adjacent fuel passages 20, andexposes this fuel to heat from the metallic surfaces heated bycombustion gases as indicated by the large arrows in FIG. 2.

Small nozzle geometry can lead to surface tension causing fuel to notonly be present at the nozzle tip, but possibly even continue to leak ordrool from nozzle 10 even after nozzle 10 has been turned off. Nozzleshut down can accentuate coking conditions beyond those when the nozzle10 is operating because the cooling flow of fuel through nozzle 10 isstopped but there is still considerable heat present in and aroundnozzle 10. And, even when the supply of exhaust is shut off, e.g., whenthe diesel engine is shut down, the heat accumulated in housing 3 thatsupports nozzle 10 flows into the cooler fuel passages 20 and intonozzle 10 itself. This is a common phenomenon called heat soak back.

Moreover, when the engine is shut off, hot exhaust ducts cool by naturalconvection. The resultant high temperature gases seek higher levels andcan accumulate around nozzle 10. This can expose stagnant fuel held bysurface tension in fuel passages 20 to temperatures in excess of thoserequired to destabilize the fuel and deposit coke. High recirculation ofhot external gases can heat the nozzle all the way to the core. If fuelis shut off, but hot external gasses persists, both primary andsecondary fuel channels will show signs of contamination unlesspreventative measures are taken.

The foregoing discussion has described various causes for coke depositsin nozzles, and the following discussion describes causes for carbondeposits. Engine running conditions are usually responsible for carbondeposits in areas with an excessive, hot fuel concentration and ashortage of air. These conditions typically occur external to, but inclose proximity to the nozzle. External carbon, as opposed to internalcoke, can accumulate near fuel nozzle orifice 30 from combustion gasesbeing entrained by the high pressure fuel spray and condensing aroundthe fuel opening. Carbon deposited on the face of nozzles is common formany pressure atomizing fuel nozzles, and it can detrimentally affectnozzle spray and flow number. Excessive combustion swirl, hotrecirculation after fuel flow is shut off, and/or hot convection flowdue to buoyancy can result in carbon deposits that affect the spray conefrom the tip of the primary nozzle, i.e., the nozzle on the centerline.Flow number will be reduced by carbon deposited on this contaminatedflare.

In short, heat sources that can be problematic for nozzles include soakback from adjacent housings or castings, recirculating combustion gasflows too close to the nozzle face, and hot gases from downstreamexhaust components that flow towards nozzles driven by buoyancy aftershut down. These heat sources tend to cause accumulation of deleteriouscoke and carbon deposits in nozzle components.

Referring now to FIGS. 3-8, an exemplary pressure atomizing nozzle 100in accordance with the present invention addresses these adverse heatingeffects. As shown in FIG. 3, an inlet housing 102 is provided for fluidconnections to nozzle 100. Inlet housing 102 is thermally isolated fromthe main combustion housing 3 to which it is mounted in use. Thisprevents undesirable heat accumulation within its mass, as will bedescribed in greater detail below. FIG. 4 shows the fluid inlets andcoolant outlet of inlet housing 102. Inlet housing 102 includes a firstfuel stage inlet 104, a second fuel stage inlet 106, a coolant fluidoutlet 108, a coolant fluid inlet 110, and a cooling air inlet 112.Internal portions of these inlets 104, 106, 110, and 112 and outlet 108are also shown in relation to their respective conduits in FIG. 3.Interior spaces are segregated from one another by elastomeric packings,such as o-rings 103. Two fuel stages are used so that during start up,only one stage provides fuel for combustion to avoid flooding, and thenthe second stage can be ignited for full power operation.

Inlet housing 102 defines an interior space 114, and is configured tothermally isolate interior space 114 from external conditions and toremain relatively cool under operation so as to substantially eliminateheat soak back from inlet housing 102 to interior space 114 afteroperation of nozzle 100. This thermal isolation is accomplished largelyby cooling of inlet housing 102 by all fluids passing therethrough intonozzle 100, including coolant flow into and out of nozzle 100. As such,inlet housing 102 remains relatively cool during engine operation andtherefore does not feed accumulated heat back into the fuel passages(i.e., heat soak back) when the engine is shut down or when the fuelflow is shut off while the high temperature gas flow remains on, e.g.,exhaust gas flow. Thus nozzle 100 and its connections are isolatedthermally from the hot adjacent housing to which nozzle 100 is mounted.In an exemplary application, inlet housing 102 stays relatively cool,never exceeding about 190° F., so it does not impose a heat soak backproblem on fuel after shut down that would lead to coke or carbondeposition.

With continued reference to FIG. 3, a first fuel conduit 116 is mountedin interior space 114 of inlet housing 102 in fluid communication withfirst fuel stage inlet 104 for providing fuel to a first pressureatomizing nozzle 118 mounted thereto. A second fuel conduit 120 ismounted in interior space 114 outboard of first fuel conduit 116 and influid communication with second fuel stage inlet 106 for providing fuelto a second pressure atomizing nozzle 122 mounted outboard of firstpressure atomizing nozzle 118.

A first coolant conduit 124 is mounted in interior space 114 outboard ofsecond fuel conduit 120 and in fluid communication with coolant fluidoutlet 108 and with nozzle tip region 126 for conducting coolant awayfrom second pressure atomizing nozzle 122. A second coolant conduit 128is mounted in interior space 114 outboard of first coolant conduit 124in fluid communication with coolant fluid inlet 110 for conductingcoolant to a nozzle tip region 126 proximate to the outlets of the firstand second pressure atomizing nozzles 118, 122 to cool nozzle tip region126.

With reference now to FIG. 5, first and second coolant conduits 124 and128 function to cool nozzle tip region 126 actively during operation andpassively after operation. During operation, engine coolant isconstantly circulated through nozzle 100 via conduits 124 and 128,reaching the extreme tip of the fuel distribution cone as indicated bythe heavy coolant flow arrows shown in FIG. 5. Coolant flows in fromcoolant conduit 128 and through radial slots 136 in first coolantconduit 124, which are shown without coolant in FIG. 6, for egress viacoolant fluid outlet 108, which is shown in FIGS. 3-4. Slots 136 areradially offset to induce swirl on coolant flowing therethrough toincrease heat transfer, and are optionally dimensioned to serve asmetering slots. Thus during engine operation, coolant is forced toimpinge on the critical cone area of nozzle tip region 126 to maintain acool environment even when fuel flow is shut off to nozzle 100. Once theengine is shut down, passive cooling results as heat reaching thecoolant at the nozzle tip causes the coolant to circulate throughbuoyancy induced forces, thus encouraging cooler liquid to replaceheated fluid. Engine coolant can be used as the coolant, or fuel or anyother suitable coolant can be used if a cool supply is available.

Referring again to FIG. 3, a cooling air conduit or jacket 130 ismounted to inlet housing 102 outboard of second coolant conduit 128 influid communication with cooling air inlet 112 for conducting a flow ofcooling air to an outlet end of second pressure atomizing nozzle 122.Cooling air jacket 130 is configured to be a heat shield and tothermally isolate inboard components from exterior conditions. Throughjacket 130, clean air is provided during engine operation to nozzle tipregion 126 for diluting carbon and thereby reducing carbon deposits onsecond pressure atomizing nozzle 122 and other components in nozzle tipregion 126. The cooling air supplied through jacket 130 provides activecooling for nozzle tip region 126 during engine operation, and jacket130 provides passive cooling to nozzle tip region 126 after engineoperation by action of buoyancy forces. The downstream face of injector100 is set in from the adjacent surface of housing 3 by small distance δto account for thermal expansion and contraction, as well astolerancing. In other words, when in a cool condition, nozzle 100contracts from being flush with housing 3 by a distance δ, and when in aheated condition, nozzle 100 expands to be flush with housing 3. In FIG.3, distance δ is exaggerated for clarity, but can be around 0.010inches, for example, depending on the application. This is beneficialbecause protrusion of a nozzle out beyond the inner surface of thehousing can sometimes increase heat transfer to the tip from the hotcombustion gases in the combustor.

Referring now to FIG. 7, hot gas including combustion products, can heatthe outer face of nozzle 100 when the nozzle 100 is operating, asindicated schematically by the flow regions in FIG. 7. In fact, thenozzle spray induces the hot gas to flow up to the actual fuel orifice132. Jacket 130 acts as a heat shield against heat from this inducedcombustor flow. The cool air from air passage 134 of jacket 130 emanatesaround fuel orifice 132 thus diluting any carbonaceous gas flow andproviding a cool buffer for the fuel nozzle surfaces. Air passage 134 isa cold air circuit that acts like an ejector to reduce or preventrecirculating combustion products from heating the nozzle face and fromcondensing around fuel orifice 132 in the form of carbon deposits. In anexemplary application, the metering hole for air passage 134 is about0.1 inches in diameter.

With reference now to FIG. 8, when the fuel flow is shut down in nozzle100, the cool flow of air continues to provide a buffer against anyreverse combustor flow. The residual pressure in the cold flow of airpassage 134 ensures during fuel-off periods only cold, clean air entersthe nozzle orifice, i.e. fuel orifice 132, as indicated by the arrows inFIG. 8. Thus, when fuel flow stops, cool, clean air will flow intonozzle 100 instead of hot exhaust or combustion products. As in the caseof the coolant flow described above, when the engine is shut off and airpassage 134 is no longer pressurized, cold air continues to circulate injacket 130 replacing any heated air within the jacket by naturalconvection and buoyancy forces for passive cooling. This naturalcirculation together with heat shield effects of jacket 130 counteractsexhaust gas buoyancy effects occurring after engine operation to keepnozzle 100 cool even after complete engine shut down. Cooling air can besupplied through jacket 130 during and between nozzle operation,however, in applications where the cooling air has a detrimental affecton fuel spray or combustion during nozzle operation, the cooling airsupply can be shut off while fuel is flowing to tip region 126.

Referring now to FIGS. 9-13, another exemplary embodiment of a nozzle200 in accordance with the present invention is described as follows. Asshown in FIG. 9, Nozzle 200 includes an inlet housing 202 having aninterior space 214, first and second fuel conduits 216 and 220, firstand second pressure atomizing nozzles 218 and 222, first and secondcoolant conduits 224 and 228, and cooling air jacket 230 much asdescribed above with respect to nozzle 100.

With reference now to FIG. 10, inlet housing 202 includes a first fuelstage inlet 204, a second fuel stage inlet 206, a coolant fluid outlet208, and a coolant fluid inlet 210, much as described above with respectto inlet housing 102. Unlike inlet housing 102 described above, inlethousing 202 does not include an air inlet. Instead, as shown in FIG. 9,air inlets 212 are provided directly through air jacket 230 to providepressurized air from an external source, e.g., filtered engine air, intoair jacket 230. Nozzle 200 has a reduced length from inlets to nozzletip compared to nozzle 100 described above, due the differentarrangement of the various inlets and conduits, allowing for reductionof the overall size envelope required.

Referring to FIG. 11, nozzle 200 includes a heat shield 229 mountedbetween second cooling conduit 228 and air jacket 230. This providesthermal isolation to protect nozzle tip region 226 from heat in the airentering through air inlets 212. While air inlets 212 supply air todilute the nozzle orifice and to provide cooling during combustion, theair supplied through air inlets 212 can be hot enough when the fuel flowis off to heat nozzle tip region 226. Heat shield 229 reduces the impactof this heat input. Air flowing in through cooling air inlets 212 flowsbetween heat shield 229 and air jacket 230 and around standoffs 231before reaching orifice 232. Standoffs 231 are configured with radiallyoffset passages therebetween to impart swirl onto a flow of airtherethrough for increasing cooling effectiveness in tip region 226.First coolant conduit 224, second coolant conduit 228, and air jacket230 all have an outlet section having a reduced, e.g., necked down,diameter to reduce the size of nozzle tip region 226 for improved heatexchange. Conduit 224 is pushed into conduit 228 with sufficient forceto elastically stretch the hole in conduit 228 and to induce a reactivespring force or interference fit which is sufficient to seal theinterface without requiring brazing or the like. The smaller thediameter of the interference, the easier it is to accomplish the elasticinterference fit and the higher the success of leak proofing becomes. Inshort, the reduced, necked down diameter in nozzle tip region 226 isadvantageous for manufacturing. Second pressure atomizing nozzle 222 ismounted over the tip portion of second fuel conduit 220 to provide anatomized spray of fuel from between first and second pressure atomizingnozzles 218 and 222. Those skilled in the art will readily appreciatethat while described herein in the exemplary context of dual orifices,it is also possible to achieve similar benefits to those describedherein using single orifice pressure atomizers without departing fromthe spirit and scope of the invention.

Referring now to FIG. 12, in order to allow coolant to egress from tipregion 226 to coolant outlet 208, facets are formed in the outer surfaceof second pressure atomizing nozzle 222 to form coolant passages 223between second pressure atomizing nozzle 222 and first coolant conduit224. The cross-section in FIG. 12 is indicated in FIG. 11. Secondpressure atomizing nozzle 222 is brazed to second fuel conduit 220, andthe braze joint is not shown in FIG. 11, but is indicated by the dashedlines in FIG. 12. The space between conduits 216 and 220 is thesecondary fuel channel.

Referring now to FIG. 13, secondary fuel flow from second fuel stageinlet 206 passes between first fuel conduit 216 and second pressureatomizing nozzle 222 through passages 217 defined in the outer surfaceof first fuel conduit 216. This allows second stage fuel to pass betweensecond pressure atomizing nozzle 222 and first fuel conduit 216 on itsway to be issued as a spray from the annular orifice between first andsecond pressure atomizing nozzles 218 and 222. Disc 219 separates thefirst and second fuel circuits from mixing together.

The devices and methods described above can be used to thoroughly coolfuel passages of nozzles both actively and passively to reduce orprevent coke accumulation, and to reduce or prevent carbon contaminationon nozzle surfaces. While described above in the exemplary context of aduplex pressure atomizing nozzle used in exhaust treatment for ahydrocarbon combustion powered engine, those skilled in the art willreadily appreciate that the devices and methods of the subject inventioncan be used in any suitable application. Moreover, the devices andmethods of the invention can be used in any suitable type of nozzle orinjector without departing from the spirit and scope of the invention.

The methods and systems of the present invention, as described above andshown in the drawings, provide for nozzles with superior propertiesincluding shielding and thermal isolation of interior passages andexterior surfaces to reduce and prevent carbon and coke deposits. Whilethe apparatus and methods of the subject invention have been shown anddescribed with reference to preferred embodiments, those skilled in theart will readily appreciate that changes and/or modifications may bemade thereto without departing from the spirit and scope of the subjectinvention.

What is claimed is:
 1. A spray nozzle, comprising: a) an inlet housingincluding a fuel inlet, wherein the inlet housing defines an interiorspace and is configured to thermally isolate the interior space fromexternal conditions during operation and to reduce heat soak back fromthe inlet housing to the interior space thereof after operation; b) afuel conduit mounted in the interior space of the inlet housing in fluidcommunication with the fuel inlet for providing fuel to a spray nozzlemounted to the fuel, conduit; and c) a cooling air jacket mounted to theinlet housing outboard of the fuel conduit and spray nozzle forconducting a flow of cooling air to nozzle tip region proximate anoutlet end of the spray nozzle wherein the cooling air jacket isconfigured to thermally isolate inboard components from exteriorconditions, to provide clean air during operation to the nozzle tipregion for diluting carbon to reduce carbon deposits on the spray nozzleand for cooling the same, and to conduct air for passive cooling of thenozzle tip region after operation, wherein the fuel conduit is a firstfuel conduit, wherein the spray nozzle is a first spray nozzle, whereinthe fuel inlet is a first fuel stage inlet, wherein the inlet housingincludes a second fuel stage inlet, and further comprising a second fuelconduit mounted in the interior space of the inlet housing outboard ofthe first fuel conduit and in fluid communication with the second fuelstage inlet for providing fuel to a second spray nozzle mounted outboardof the first spray nozzle.
 2. A spray nozzle as recited in claim 1,wherein the inlet housing includes a cooling air inlet in fluidcommunication with an air flow circuit within the cooling air jacket forsupplying cooling air during operation.
 3. A spray nozzle as recited inclaim 1, wherein the cooling air jacket includes a cooling air inlet influid communication with an air flow circuit within the cooling airjacket for supplying cooling air during operation.
 4. A spray nozzle asrecited in claim 1, further comprising: d) a coolant conduit mountedoutboard of the fuel conduit for circulating coolant in the nozzle tipregion for cooling the spray nozzle; and e) heat shield mounted inboardof the cooling air jacket and outboard of the coolant conduit to providethermal isolation therebetween.
 5. A. spray nozzle as recited in claim1, wherein the cooling air jacket includes an outlet aperture inproximity with the spray nozzle for providing an outlet for the spraynozzle and cooling air.